Cold cathode gas discharge tubes



United States Patent 3,135,892 C611) CATHODE GAS DISCHARGE TUBES Georgehater Stenning, Stanmore, lxiddlesex, England, assignor to HivacLimited, South Ruislip, Middlesex, England, a company of Great BritainFiled Dec. 4, 1961, Ser. No. 155,579 Claims priority, application GreatBritain Dec. 8, 1969 8 Claims. (Cl. 313-438) This invention relates tocold cathode gas discharge tubes and is more particularly concerned withtubes of the so-called trigger type in which breakdown of the maindischarge path between the cathode and anode of the tube is initiated bya triggering discharge brought about by application of a suitablecontrol potential to a further or trigger electrode.

In accordance with the broadest aspect of the invention, the cathodeelectrode is of small size relative to the cooperating anode and islocated within and is eifectively surrounded by such anode while thetrigger electrode is arranged at a suitable small spacing distance fromsaid cathode in between it and said anode.

in a preferred form of construction according to the invention, theanode has the shape of a cylinder which may be open-ended but which ispreferably at least partially closed at one or both ends while thecathode has the form of a rod or fiat plate disposed within and co-arialwith said anode. The trigger electrode may conveniently comprise afurther cylinder co-axial with but of smaller diameter and of lesseraxial length than said anode and surrounding at least a part of thecathode. The actual trigger gap is constituted in a preferred form by awirelike extension from the trigger electrode cylinder passing intoclose-spaced relationship with the cathode at a position adjacent anopen end of the trigger cylinder.

In an alternative construction the anode may be of semispheiical formwith the cathode disposed substantially at the centre point of the anodesurface.

In order that the nature of the invention may be more readilyunderstood, a number of particular constructional embodiments thereofwih now be described by way of illustrative example only and withreference to the accompanying drawings in which:

FIG. 1 is a largely schematic axial sectional view of one form of coldcathode discharge tube according to the invention;

FIG. 2 is an enlarged end View of the electrode structure of the tubeshown in FIG. 1;

FIGS. 3 and 4 are axial sectiona views of other alternative forms ofelectrode structure according to the invention.

Referring first to FIGS. 1 and 2 of the drawings, the tube constructionshown therein comprises a cathode 1G in the form of a rectangularcross-section metal strip having a somewhat pointed upper end 11. Thiscathode strip is attached to an electrode support Wire 12 which isembedded within a moulded glass stem 13 integral with a button orplatform 14 serving as a mouting for all of the tube electrodes. Thewire 12 passes, in the usual way, to an external connection lead 25extending outwardly from the tube envelope shown at 26.

The anode 15 is in the form of an almost, but preferably not quite,complete cylinder 16 of sheet metal which is seated at its lower endupon or in close-spaced relationship to the upper surface of theplatform 14 and is closed at its opposite upper end by a closure wall 17which is preferably of domed shape as shown. The anode is secured inposition by interconnection with support/connection wires 18 which aremoulded in the platform 14 and at least one of which passes to anexternal connection lead 25.

3,135,892 Patented June 2, 1964 The trigger electrode 19 is in the formof a further imperforate sheet metal cylinder co-axial with the anode 15and cathode 16, said trigger electrode cylinder surrounding the cathodeand extending from the upper surface of the platform 14 to a regionapproximately level with the upper end 11 of the cathode 10. To suchcylinder 19 is attached an inwardly directed wire portion 20 which ispositioned, as by bending, to pass close to the pointed end 11 of thecathode thereby to provide a trigger gap of small dimension betweenitself and the said cathode. The trigger gap is thus readily visiblefrom a major area of the anode, a known requirement for reliable andconsistent triggering of the main discharge within the tube. The triggerelectrode is attached to a support/ connection wire 21 which is alsomoulded in the platform 14 and extends to another external connectionlead 25.

The tube is provided with a further keep alive electrode in the form ofan auxiliary cathode 22 disposed in close-spaced relationship to theinner surface of the anode cylinder 16. This keep alive electrode isattached to a support/connection wire 23 also moulded into the platform14 and thereafter joined to a further external connection lead 25.

The cathode 15 may be of pure metal such as molybdenum but other metals,such as nickel or tantalum, normally used for cathode construction ofcold cathode gas discharge tubes may be employed. Alternatively thecathode may be one coated with emissive material. The cathode isarranged to have sufiicient outer surface area to carry the value ofcurrent desired to flow through the tube; in order to avoid the need foran inconveniently large cathode area having to be located at the centreof the surrounding anode, a relatively high gas filling pressure may beemployed in some applications where large current values are desired.Such gas filling may be, for example, of neon or a mixture composedprincipally of neon with about 1% of argon, krypton or helium.Alternatively, for some applications, a filling consisting wholly ormainly of one of the inert gases, or even hydrogen, may be used. Thefilling may be at a pressure of 200-300 mm. Hg instead of the more usualpressure of 3050 mm. Hg for many applications although the more usualpressures of the last mentioned range may be used for some applications.

The arrangement of the cathode it to lie at the centre of a surroundingand substantially enclosing anode 15 has the advantage of providing ahigh potential gradient at the cathode which is conducive to eficiencyof electron emission and sensitivity to triggering by a small currentdischarge between the trigger electrode and the cathode. Thecorrespondingly low potential gradient at the anode renders the actualshaping of the anode structure non-critical. Furthermore, both thecathode and the trigger electrodes are enclosed and effectively shieldedby the anode which is the electrode least sensitive to externalinfluences.

The provision of a keep alive electrode operating in the low potentialgradient conditions immediately adjacent the auode enables it to performthe function of providing ionisation without causing risk of undesiredbreakdown between the cathode and anode. The pres ence of the triggerelectrode, which is connected to a potential intermediate that of theanode and cathode, largely surrounding the cathode, constitutes meansfor providing a more uniform potential gradient between the cathode andanode and in consequence of this a higher operating potential may beemployed between anode and cathode for a given physical spacing distancebetween the electrodes and a given gas filling pressure. The use of ahigher gas pressure also has the advantage tially so.

' -29 of providing a higher gap breakdown voltage and a shorter recoveryor de-ionisation time.

Various modifications may be made without departing from the scope ofthe invention. Thus the anode need not physically enclose the cathodeand trigger electrodes provided it is so shaped that it effectivelysurrounds the latter electrodes by its electrostatic field. This may beachieved by extending the axial length of the anode beyond therespective ends of the trigger and cathode electrodes whereby the latterare located right inside the anode as shown in FIG. 3. Another possiblearrangement is shown in FIG. 4 where the metallic top closure wall 17 ofthe anode shown in FIGS. 1 and 2 is replaced by an insulating, e.g.mica, disc 27 which also serves in the customary manner to assist in thelocation of the electrode structure within the surrounding tube envelope26. In this further embodiment,

the mounting platform 1 is replaced by the more conventional flat pinchconstruction as shown at 28 within which the various connecting andsupport wires are embedded. As a result of this, the lower end oftheanode cylinder 16 is not completely closed but remains substan- Thetrigger electrode cylinder 19 preferably remains closed by being seatedupon the upper surface of the pinch region 23.

I claim: 7

l. A cold cathode gase discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary cathode located within a sealedenvelope containing a low pressure gaseous filling ofan inert rare gas,said cathode being of small size relative to said anode, said triggerelectrode being closely spaced relative to and substantially surroundingsaid cathode, said anode substantially surrounding said cathode andtrigger electrode and being spaced at a large. distance from the triggerelectrode compared with the spacing distance between said triggerelectrode and said cathode whereby a discharge between said triggerelectrode and cathode can be initiated at a low voltage compared withthe voltage required to cause breakdown between said anode and cathodeor beween said anode and trigger electrode and said auxiliary cathodebeing of small size compared with said cathode electrode and beingmounted in close proximity to the inner surface of said anode betweensaid anode and said trigger electrode whereby a very low current primingdischarge can be continuously maintained between said anode and saidauxiliary cathode to provide fast operation of the tube with shortvoltage pulses applied to said trigger electrode.

2. A cold cathode gas discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary cathode located within a sealedenvelope containing a low pressure gaseous filling, said cathode beingof small size relative to said anode, said trigger electrode beingclosely spaced relative to and substantially surrounding said cathode,said anode substantially surrounding said cathode and trigger electrodeand being spaced at a large distance from the trigger electrode comparedwith the spacing distance between said trigger electrode and saidcathode whereby a discharge between said trigger electrode and cathodecan be initiated at a low voltage compared with the voltage required tocause breakdown between said anode and cathode or between said anode andtrigger electrode, said auxiliary cathode being of small size comparedwith said cathode and being mounted in close proximity to the innersurface of said anode between said anode and said trigger electrodewhereby a very low current priming discharge can be continuouslymaintained between said anode and auxiliary cathode, and said gaseousfilling comprising an ionisable medium including at least one of therare gases to provide fast operation of the tube with short voltagepulses applied to said trigger electrode.

3. A cold cathode gas discharge tube comprising a ti. cathode, an anode,a trigger electrode and an auxiliary cathode located within a sealedenvelope containing a low pressure gaseous filling, said cathode beingof small surface area relative to said anode, said trigger electrodebeing closely spaced relative to and substantially surrounding saidcathode, said anode substantially surrounding said cathode and triggerelectrode and being spaced at a large distance from the triggerelectrode compared with the spacing distance between said triggerelectrode and said cathode whereby a discharge between said triggerelectrode and cathode can be initiated at a low-volage compared with thevoltage required to cause breakdown between said anode and cathode orbetween said anode and trigger electrode, said auxiliary cathode beingof small area compared with said cathode and being mounted in closeproximity to the inner surface of said anode between said anode and saidtrigger electrode whereby a very low current priming discharge can becontinuously maintained between said anode and auxlow pressure gaseousfilling, said cathode being ofsmall surface area relative to said anode,said trigger electrode being closely spaced relative to and surroundingsaid cathode, said anode substantially surrounding saidcathode andtrigger electrodes and being spaced at 'a large distance from thetrigger electrode compared with the spacing distance between saidtrigger electrode and said cathode whereby a discharge between saidtrigger electrode and cathode can be initiated at a low voltage com!pared with the voltage required to cause breakdown between said anodeand cathode or between said anode and trigger electrode, said auxiliarycathode being of small surface area compared with said cathode and beingmounted parallel with and in close proximity to the inner surface ofsaid anode whereby a very low current priming discharge can becontinuously maintained between said anode and auxiliary cathode, andsaid gaseous filling comprising not less than 99% neon at a pressure ofthe order of 20030O mm. Hg to provide fast operation of the tube withshort voltage pulses applied between said trigger electrode and saidcathode.

5. A cold cathode gas discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary athode located within a sealedenvelope containing a low 7 pressure ionisable gaseous filling, saidcathode being in the form of a short rod-like member having a surfacearea many times smaller than said anode, said trigger electrode being animperforate cylinder closely spaced relative to and surrounding saidcathode, said anode surrounding and enclosing said cathode and triggerelectrodes and being spaced at a large distance from the triggerelectrode compared with the spacing distance between said triggerelectrode and said cathode whereby a discharge between said triggerelectrode and cathode can be initiated at a low voltage compared withthe voltage required to cause reakdown between said anode and cathode orbetween said anode and trigger electrode and said auxiliary cathodebeing of smaller surface area than said cathodeelectrode and beingmounted in close proximity to the inner surface of said anode betweensaid anode and said trigger electrode whereby a very low current primingdischarge can be continuously maintained between said anode and saidauxiliary cathode to provide fast operation of the tube with shortvoltage pulses applied between said trigger electrode and said cathode.

6. A cold cathode gas discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary cathode electrode in a sealedenvelope, in which said anode is in the form of a cylinder closed ateach end and surrounding all of the other electrodes, said cathode is inthe form of a linear element of a length short compared with that of theaxial length of said anode and disposed co-axial with said anode atapproximately the centre of the anode length, said trigger electrode isalso of cylindrical shape and disposed co-axial with said cathode andanode, said trigger electrode being of imperforate character and of adiameter such that the radial spacing dis tance between said cathode andsaid trigger electrode is small compared with the radial spacingdistance between said trigger electrode and said anode and saidauxiliary cathode comprising a plate of a size small compared with thatof such cathode and which is located in parallel relationship to theinner surface of said anode with a spacing distance which is smallcompared with the spacing distance between said cathode and triggerelectrode, and in which said envelope contains an ionisable gaseousfilling comprising at least 99% neon at a pressure of the order of200300 mm. Hg.

7. A cold cathode gas discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary cathode electrode all mounted on acommon platform of insulating material in a sealed envelope, in whichsaid anode is in the form of an imperforate sheet metal cylinder seatedby one end on said platform and closed at its other end so as tosurround all of the other electrodes, said cathode is in the form of alinear element of a length short compared with that of the axial lengthof said anode and disposed co-axially within said anode at approximatelythe centre thereof, said trigger electrode is also of cylindrical shapeand disposed co-axially With said cathode and anode with one end seatedon said platform and its opposite end level with one end of said cathodeelement, said trigger electrode being of imperforate character and of adiameter such that the radial spacing distance between said cathode andsaid trigger electrode is small compared With the radial spacingdistance between said trigger electrode and said anode and saidauxiliary cathode comprising a plate having an area small compared withthat of such cathode and located in parallel relationship to the innersurface of said anode with a spacing distance which is small comparedwith the spacing distance between said cathode and trigger electrode,said sealed envelope containing a gaseous filling comprising at least99% neon at a pressure of the order of 200-300 mm. Hg.

8. A cold cathode gas discharge tube comprising a cathode, an anode, atrigger electrode and an auxiliary cathode electrode all mounted on aplatform of insulating material in a sealed envelope, in which saidanode is in the form of an imperforate metal cylinder seated at one endon said platform and closed at its other end by an imperforate metalwall so as to surround all of the other electrodes, said cathode is inthe form of a metal strip pointed at one end and of a length shortcompared with that of the axial length of said anode and disposedcoaxially within said anode at approximately the centre thereof, saidtrigger electrode is also of cylindrical shape and disposed co-axiallywith said cathode and anode with one end level with the pointed end ofsaid cathode, said trigger electrode being of imperforate character andof a diameter such that the spacing between the cathode and sad triggerelectrode is small compared with the spacing between said triggerelectrode and said anode, said trigger electrode having a wire extensionprojecting inwardly to lie close to the pointed end of said cathode, andsaid auxiliary cathode comprising a plate having a surface area smallcompared with that of such cathode and located in parallel close spacedrelationship to the inner surface of said anode, said sealed envelopehaving gaseous filling of an ionisable rare gas.

References Cited in the file of this patent UNITED STATES PATENTS

1. A COLD CATHODE GASE DISCHARGE TUBE COMPRISING A CATHODE, AN ANODE, ATRIGGER ELECTRODE AND AN AUXILLIARY CATHODE LOCATED WITHIN A SEALEDENVELOPE CONTAINING A LOW PRESSURE GASEOUS FILLING OF AN INERT RARE GAS,SAID CATHODE BEING OF SMALL SIZE RELATIVE TO SAID ANODE, SAID TRIGGERELECTRODE BEING CLOSELY SPACED RELATIVE TO AND SUBSTANTIALLY SURROUNDINGSAID CATHODE, SAID ANODE SUBSTANTIALLY SURROUNDING SAID CATHODE ANDTRIGGER ELECTRODE AND BEING SPACED AT A LARGE DISTANCE FROM THE TRIGGERELECTRODE COMPARED WITH THE SPACING DISTANCE BETWEEN SAID TRIGGERELECTRODE AND SAID CATHODE WHEREBY A DISCHARGE BETWEEN SAID TRIGGERELECTRODE AND CATHODE CAN BE INITIATED AT A LOW VOLTAGE COMPARED WITHTHE VOLTAGE REQUIRED TO CAUSE BREAKDOWN BETWEEN SAID ANODE AND CATHODEOR BETWEEN SAID ANODE AND TRIGGER ELECTRODE AND SAID AUXILIARY CATHODEBEING OF SMALL SIZE COMPARED WITH SAID CATHODE ELECTRODE AND BEINGMOUNTED IN CLOSE PROXIMITY TO THE INNER SURFACE OF SAID ANODE BETWEENSAID ANODE AND SAID TRIGGER ELECTRODE WHEREBY A VERY LOW CURRENT PRIMINGDISCHARGE CAN BE CONTINUOUSLY MAINTAINED BETWEEN SAID ANODE AND SAIDAUXILIARY CATHODE TO PROVIDE FAST OPERATION OF THE TUBE WITH SHORTVOLTAGE PULSES APPLIED TO SAID TRIGGER ELECTRODE.